UPDATE 14.11.2016:
See article with detailed instructions in MAKE magazine:
http://makezine.com/projects/3d-print-electric-unicycle/

This is an updated version of the E14D Electric Unicycle which I published earlier. My goal was to make a more compact version with better ergonomics but with the same impressive range and performance as its predecessor. This unicycle is also designed for the high performance 14" 500W Unicycle motor from Microworks, but it can be used with others as well.

The old version was designed to be used with up to 4 individual 16 cell battery packs, which were connected in parallel. Instead of 4 packs of 16 cells (16S1P), this new version uses 2 packs of 32 cells (16S2P), which makes it possible to make the battery housings significantly smaller but still with the same total capacity. Also, this version uses a horizontal controller which is located just underneath the handle, so the housings on both sides are now available for batteries.

The essential structure is the same as on the earlier version, the housings on both sides are identical and printed in two sections, which are then stacked and secured with M8 threaded rods which go through the whole structure from top to bottom. The housings on both sides are bolted to each other through the top handle part, also using two M8 threaded rods. A horizontally programmed mainboard can be placed in the space underneath the top handle. The upper nuts are now recessed and hidden inside the top covers. The 8mm bolt holes on the upper covers don´t go all the way through to the recessed nut, but there is 0.5mm of material left inbetween which needs to be drilled out. This is simply because the print result is better this way.

With the motor I used, top speed is around 30 km/h (can be limited by software to meet local legal requirements) and when using the maximum amount of battery capacity, your range should be around 40 km in actual road conditions.

I´ve been trying to keep the design as simple, compact and smooth as possible.

I recommend PLA for this project to avoid warping issues. You could also use PETG, which will be even stronger. No supports or rafts needed. Please be aware that these parts are large and will take a long time to print.

See videos:
https://www.youtube.com/watch?v=A3gQpAUEFJo&feature=youtu.be
https://www.youtube.com/watch?v=UAJHFsctif8
https://www.youtube.com/watch?v=TBEu8ykEiAg

Assembly parts needed:

• 2 rolls (à 1 kg) of PLA (or PETG) filament

• M8 threaded rods:
  4x 225mm length
  2x 60mm length

• 12x M8 nuts (13mm, nylocks recommended, you could also use cap nuts for four of them on the top covers)
• 8x M8 washers
• 12x M5 screws, approx. 12mm long (heads as flat as possible)
• 12x M5 washers
  The M8 rods&nuts could be replaced with an American thread of similar size (5/16?), but make sure that the openings for the upper nuts will fit. They are made for 13mm sized nuts, so the opening is 13.5mm. The shorter rods which are used to bolt together the handle and the two upper sections of the battery housings are less critical regarding nut size.
  The M5 threaded screws cannot be replaced as they are used on the pedal assembly which has metric threads.

Parts to be ordered (mine came from Shenzen Microworks, they can be found on alibaba):

• 14” 500W high speed motor
• standard 14”x2.125 or wider 14"x2.5 tire & inner tube
• 30B4 high speed controller with bluetooth module, please ask for horizontal programming! That will make it possible to mount the controller flat on top. You can also use a regular vertical controller, but you will then need to use one of the battery housings to accomodate the controller so you will only be able to use half of the potential battery capacity.
• pedals and assembly parts
• power switch, charging socket, LED-battery indicators, HAL-cables

Batteries:

• 2x 60 Volt 16S2P unicycle battery with 32 cells for maximum range and capacity (you can use the regular 16 cell batteries which are easier to find, but they will have only half the capacity, which is still not bad if you use two of them). Check the dimensions of the batteries (maximum thickness 43mm, max width 142mm. max height 160mm) and make sure they will fit before you buy them. It is a tight fit.
• 1 x 67 Volt generic unicycle battery charger

Other parts:

• 1-2 piezo buzzers (you can decide whether to use just one or one on each side)

IMPORTANT: MAKE ABSOLUTELY SURE BOTH BATTERIES HAVE EXACTLY THE SAME VOLTAGE BEFORE CONNECTING THEM IN PARALLEL! ALSO, DURING ASSEMBLY MAKE SURE THAT NO METAL PARTS ARE IN DIRECT CONTACT WITH THE BATTERY! DO NOT WORK ON LITHIUM BATTERIES UNLESS YOU ARE ABSOLUTELY SURE YOU KNOW WHAT YOU ARE DOING, UNDERSTAND THE RISKS AND TAKE ALL NECESSARY PRECAUTIONS! ANYTHING YOU DO HAPPENS AT YOUR OWN RISK!

UPDATE 13.10.2016:

Following updates have been made to the files:

1. Screw locations on the pedal brackets have been adjusted to match the latest version of the pedal holder from Microworks.
2. Upper covers have been changed to fit the latest version of the LED battery indicators from MIcroworks (LEDs directly on PCB)
3. Battery housings have been slightly widened on the inside to easier fit 32 cell packs on both sides (43.5mm width).
4. The space for the controller board underneath the handle has been made slightly higher.
5. Both halves of the battery housings have been made slightly higher, adding just enough clearance to also use a wider 14x2.5" tire instead of the regular 14x2.125". The outer diameter of the 14x2.5" tire will in fact make this a 15" unicycle.

This unicycle shell can now also be used with 16" motors if you use the following spacer, which can be added between upper and lower section of the battery housing to increase overall height:
http://www.thingiverse.com/thing:1834059

9.11.2016:
Now you can also add some fenders with or without integrated headlight:
http://www.thingiverse.com/thing:1879793

PLEASE SHARE YOUR MAKE IF YOU DECIDE TO PRINT THIS ITEM!

CREATING AND FINALIZING THIS ELECTRIC UNICYCLE HAS TAKEN SEVERAL WEEKS OF DESIGNING, TESTING, MODIFICATIONS AND MORE THAN A DOZEN TEST VERSIONS TO GET ALL THE PARTS RIGHT AND TO MAKE THEM FIT PERFECTLY. PLEASE CONSIDER LEAVING A TIP VIA THINGIVERSE IF YOU FIND THIS ITEM USEFUL.